JP2003089526A - Lithium nickel manganese multiple oxide, positive electrode material for lithium secondary cell by using the same, positive electrode for lithium secondary cell, and lithium secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lithium nickel manganese multiple oxide which can be used for a lithium secondary cell excellent in the discharge capacity with a large current and having high volume energy density. SOLUTION: The lithium nickel manganese multiple oxide is expressed by the formula (1): LiXNiYMnZQ(1- Y- Z) O2 and has <=3.5 m<2> /g specific surface area and 1.4 to 2.8 g/cm<3> packing density of the powder. In the formula (1), X represents a number in the range of 0<X<=1.2, Y and Z satisfy the relations of 1<=Y/Z<=9 and 0<(1-Y-Z)<=0.5, and Q represents at least one kind selected from Co, Al, Fe, Mg, Ga, Ti and Ca.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a lithium nickel manganese composite oxide, a positive electrode material for a lithium secondary battery, a positive electrode for a lithium secondary battery, and a lithium secondary battery using the same.

[0002]

2. Description of the Related Art In recent years, as portable electronic devices and communication devices have become smaller and lighter, there has been a demand for a secondary battery having high output and high energy density as a power source thereof. In addition, as a power source for automobiles, a secondary battery having the above characteristics is required. In particular, lithium secondary batteries meet the above requirements and are being rapidly developed.

As a positive electrode active material of a lithium secondary battery,
LiCoO ₂ , LiNiO ₂ , LiMn ₂ O _{4 and} other lithium composite oxides have been proposed and actively researched. Among these, LiCoO ₂ is mainly used from the viewpoint of easiness of synthesis, operating voltage, discharge capacity and the like. However, Co is a resource-poor and expensive element. On the other hand, LiMn ₂ O ₄ is attractive because of its rich reserves, but it is necessary to solve the cycle characteristics and storage characteristics at high temperatures for practical use. In addition, LiNiO
₂ is superior to Co in terms of raw material cost, and LiCoO ₂
Although there is a possibility that a discharge capacity that exceeds the above may be obtained, improvements are needed in terms of atmosphere control and safety during firing and storage.

J. Mater. Chem. 6 (199
6) p. 1149, J. Electrochem.
Soc. 145 (1998) p. In 1113, Ni
LiNi _1-x Mn _x O with a part of the site replaced by Mn
₂ (0 ≦ x ≦ 0.5) has been improved, but M
There is a problem that a sufficient capacity cannot be obtained when the n-substitution amount is increased. Furthermore, the 41st Battery Symposium 2D20
In (2000), Ni: Mn = corresponding to x = 0.5.
It is reported that a highly crystalline single phase having a 1: 1 layered structure was synthesized by a coprecipitation method.

[0005]

Among the above, the lithium nickel man composite oxide in which a part of the nickel site is replaced with manganese is a material to be noted in terms of safety and resources. However, according to the study of the present inventors, the lithium nickel manganese composite oxide as described above has a low powder packing density and a high specific surface area when an attempt is made to obtain a large discharge capacity at a high current density. As a result, it has been found that not only is it difficult to form a practical electrode, but there is a problem that the energy density per volume in the battery is reduced. On the other hand, if the powder packing density is high and the specific surface area is low, a sufficient discharge capacity cannot be obtained at a high current density.

[0006]

Means for Solving the Problems As a result of intensive studies on the improvement of the above-mentioned lithium nickel manganese composite oxide, the present inventors have found that transition metal sites containing a nickel atom and a manganese atom are different elements (hereinafter, Such a problem can be solved by partially substituting the element for substitution of such transition metal site with "substitution element") and controlling to a specific specific surface area and powder packing density. And completed the present invention.

That is, the gist of the present invention is the following general formula (1)
Lithium-nickel-manganese composite oxide represented by, having a specific surface area of 3.5 m ² / g or less and a powder packing density of 1.4-2.8 g / cm ^3. It exists in a manganese composite oxide, and a positive electrode material, a positive electrode and a lithium secondary battery using the same.

[0008]

Embedded image Li _X Ni _Y Mn _Z Q _(1-YZ) O ₂ (1) (In the formula, X represents a number in the range of 0 <X ≦ 1.2. Y and Z are 1 ≦ Y / Z ≦ 9 and 0 <(1−Y−Z) ≦
It represents a number that satisfies the relationship of 0.5. Q is Co, Al, F
represents at least one selected from the group consisting of e, Mg, Ga, Ti and Ca. )

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The lithium-nickel-manganese composite oxide of the present invention is an oxide having a layered crystal structure and containing lithium, nickel, manganese, nickel, and an element other than manganese. The atomic ratio of nickel to manganese is 1 ≦ Ni / Mn ≦ 9, preferably 1 ≦, from the viewpoint that the layered crystal structure is stable and the battery characteristics are not deteriorated.
Ni / Mn ≦ 8, more preferably 1 ≦ Ni / Mn ≦ 7
And

One of the features of the present invention is that a substituting element is present at the site where nickel and manganese are present. Generally, lithium nickel manganese composite oxide is
The specific surface area is relatively large relative to the powder packing density, resulting in poor volume energy density and coatability, while the powder packing density is small relative to the specific surface area, resulting in poor discharge capacity at large currents. There is a tendency. Therefore, the value of the specific surface area described later is 3.5 m ² / g or less, and the powder packing density is 1.4.
It was difficult to set it to −2.8 g / cm ³ . However, by including a substitutional element, the specific surface area is relatively low with respect to the powder packing density and the powder packing density is relatively high with respect to the specific surface area, that is, the specific surface area is 3. 5 m ² / g or less and a powder packing density of 1.4-
It becomes easy to set it as 2.8 g / cm ³ .

As the substituting element, cobalt, aluminum, cobalt, iron, magnesium, gallium, titanium,
Calcium is used. Among these, cobalt, aluminum and magnesium are preferable, cobalt and aluminum are more preferable, and cobalt is the most preferable. Cobalt, aluminum, and magnesium have the advantage that they can be easily solid-dissolved in the lithium nickel manganese composite oxide to obtain a single phase. Further, cobalt and aluminum have high performance as positive electrode active materials for lithium secondary batteries. It has the advantage of exhibiting excellent battery characteristics, particularly good discharge capacity retention rate after repeated charging and discharging.
Cobalt has the advantage of exhibiting high performance battery characteristics, particularly good storage characteristics. Of course, a plurality of these metal elements may be used.

The atomic ratio of the substituting element to the total of the substituting element, nickel and manganese is usually 0.5 or less, preferably 0.4 or less, more preferably 0.35 or less. If the replacement ratio is too large, the capacity when used as a battery material tends to decrease. However, if the substitution ratio is too low, the effect of improving the cycle characteristics may not be sufficiently exerted.
Or more, preferably 0.02 or more, more preferably 0.
05 and above. If the atomic ratio is too small, the value of the specific surface area becomes too large with respect to the powder bulk density, and it becomes difficult to control the specific surface area and the powder packing density value specified in the present invention. If the atomic ratio is too large, the discharge capacity tends to decrease.

The lithium nickel manganese composite oxide of the present invention is represented by the following general formula (1).

[0014]

Embedded image Li _X Ni _Y Mn _Z Q _(1-YZ) O ₂ (1) Here, in the formula (1), X is 0 <X ≦ 1.2, preferably 0 <X ≦ 1.1. Represents the number of ranges. If X is too large, problems such as generation of different phases, destabilization of crystal structure, and reduction in battery capacity of a lithium secondary battery using the same occur. Y and Z are numbers satisfying Y + Z <1, and 1
It represents a number in the range of ≦ Y / Z ≦ 9.

The value of (1-Y-Z) is 0.5 or less, preferably 0.4 or less, more preferably 0.35 or less. When the amount of the substituting element is too large, the battery capacity of the lithium secondary battery using the lithium nickel manganese composite oxide as the positive electrode active material may be significantly reduced. However, if the substitution ratio is too small, the powder properties such as the powder packing density are deteriorated, so that the value of (1-Y-Z) is usually 0.
It is set to 01 or more, preferably 0.02 or more, and more preferably 0.05 or more. Q is Al, Co, Fe, Mg, G
It represents at least one selected from the group consisting of a, Ti and Ca. Of these, preferred are Co, Al and M.
g, more preferred are Co and Al, and most preferred is Co. Co, Al and Co are LiNi _1-x M
It can be easily solid-dissolved in n _x O ₂ (0.7 ≦ Ni / Mn ≦ 9) and synthesized as a single-phase lithium-transition metal composite oxide. Further, regarding Co and Al, the lithium secondary battery using the obtained lithium-transition metal composite oxide as a positive electrode active material is excellent in high-performance battery characteristics, in particular, in discharge capacity retention rate when repeatedly charged and discharged. Show performance. With regard to Co, particularly good performance is exhibited with respect to storage characteristics.

In the composition of the above general formula (1), the oxygen content may have some nonstoichiometry. Also, L
It may have an element other than i, Ni, Mn and the element Q. The powder packing density (tap density after 200 taps) of lithium nickel manganese composite oxide is 1.4 g / cm.
^{It is 3} or more, preferably 1.5 g / cm ³ or more. Also,
Usually 2.8 g / cm ³ or less, preferably 2.6 g / cm ³
It is the following. If the powder packing density is too low, the capacity per volume of the electrode is low, so that the capacity of the battery decreases. On the other hand, if it is too high, the porosity tends to decrease, and the capacity at high current density decreases. The powder packing density is not limited to the composition of the positive electrode active material such as the substitution amount of the substitution element and the molar ratio of nickel and manganese,
It can be controlled by manufacturing conditions such as drying conditions and firing conditions.

[0017] The specific surface area of the lithium-nickel-manganese composite oxide, 3.5 m ² / g or less, preferably 2.5 m ² /
g or less. Further, it is usually 0.2 m ² / g or more, preferably 0.3 m ² / g or more, more preferably 0.33 m ²
/ G or more. If the specific surface area is too high, there arises a problem that the conductive matrix is difficult to form when a certain amount of the conductive agent is added per weight, and if it is too low, coarse particles are formed and the capacity at high current density is lowered. The specific surface area can be controlled by the manufacturing conditions such as the drying condition and the firing condition other than the composition of the positive electrode active material such as the substitution amount of the substituting element and the molar ratio of nickel and manganese.

In the present invention, the specific surface area of the lithium nickel manganese composite oxide is known as BET.
It is measured by a powder specific surface area measuring device. The measurement principle of this method is as follows. That is, the measurement method is the BET one-point method measurement by the continuous flow method, and the adsorption gas and carrier gas used are nitrogen, air, and helium. The powder sample is heated and degassed with the mixed gas at a temperature of 450 ° C. or lower, and then cooled with liquid nitrogen to adsorb the mixed gas. This is heated with water to desorb the adsorbed nitrogen gas, which is detected by a thermal conductivity detector, the amount of which is determined as a desorption peak, and calculated as the specific surface area of the sample.

The lithium nickel manganese composite oxide is
The average primary particle size is usually 0.01 μm or more, preferably 0.02 μm or more, more preferably 0.1 μm or more, usually 30 μm or less, preferably 5 μm or less, more preferably 2 μm or less. The average secondary particle diameter is usually 1 μm or more, preferably 4 μm or more, usually 50 μm or less, preferably 40 μm or less.

Lithium nickel manganese composite acid of the present invention
Compounds are, for example, lithium, nickel, manganese, and other gold
It can be manufactured by firing a raw material containing a group element.
You can As a lithium source used as a raw material,
For example, Li₂CO₃, LiNO₃, LiOH, LiOH
・ H₂O, lithium dicarboxylate, lithium citrate,
Fatty acid lithium, alkyl lithium, lithium halogen
Examples thereof include various lithium compounds such as compounds.
More specifically, for example, Li₂CO₃, LiNO₃, L
iOH, LiOH / H₂O, LiCl, LiI, acetic acid L
i, Li₂O and the like can be mentioned. These lithium
Among the raw materials, Li is preferable.₂CO₃, LiNO ₃, L
iOH / H₂Water-soluble lithium compounds such as O and Li acetate
Is. These water-soluble compounds are used as a dispersion medium, for example.
Volume by dissolving it in a slurry using water.
Lithium nickel manganese composite with easily good properties
An oxide can be obtained. In addition, when firing, NO
x and SOx do not generate harmful substances such as nitrogen
Preferred are lithium compounds containing no child or sulfur atom.
The most preferred lithium source is also water soluble,
LiOH / H containing no elementary or sulfur atoms₂Is O
It Of course, even if you use multiple types of lithium sources
Good.

As the nickel source, for example, Ni (O
H)₂, NiO, NiOOH, NiCO₃・ 2Ni (O
H)₂・ 4H₂O, NiC₂O_Four・ 2H₂O, Ni (NO₃)
₂・ 6H ₂O, NiSO_Four, NiSO_Four・ 6H₂O, fatty acid
Selected from the group consisting of nickel and nickel halides
You can list at least one that was exposed. In this
Also emits harmful substances such as NOx and SOx during the firing process.
N-containing no nitrogen or sulfur atoms, because it does not grow
i (OH)₂, NiO, NiOOH, NiCO₃・ 2Ni
(OH)₂・ 4H₂O, NiC₂O_Four・ 2H₂D like O
The Heckel compound is preferred. In addition, as an industrial raw material
From the viewpoint of being cheaply available and having high reactivity
Ni (OH) is particularly preferable.₂, NiO, NiO
It is OH. Of course, multiple sources of nickel are used.
May be used.

As the manganese source, for example, Mn ₃ O ₄ ,
Mn ₂ O ₃ , MnO ₂ , MnCO ₃ , Mn (NO ₃ ) ₂ , Mn
Examples include SO ₄ , manganese dicarboxylate, manganese citrate, fatty acid manganese, manganese oxyhydroxide, manganese hydroxide, and manganese halide. Among these manganese raw materials, Mn ₂ O ₃ , Mn ₃ O ₄
Is preferable because it has a valence close to the manganese oxidation number of the final target compound oxide. Further, Mn ₂ O ₃ is particularly preferable from the viewpoint of being inexpensively available as an industrial raw material and from the viewpoint of high reactivity. The manganese source may be manganese ion generated by ionizing a manganese compound in the slurry. Of course, plural kinds of manganese sources may be used.

As the source of the substitutional element, the substitution metal
Carbonate in addition to hydroxide, oxide, hydroxide, halogen
Inorganic acid salts such as salts, nitrates, sulfates, acetates, oxalic acid
Examples thereof include organic acid salts such as salts. Concrete aluminum
Examples of the source of nickel include AlOOH and Al₂O₃, A
l (OH)₃, AlCl₃, Al (NO₃)₃・ 9H₂O and
And Al₂(SO_Four)₃Various aluminum compounds such as
You can get it. Above all, NOx and
In terms of not generating harmful substances such as SOx, AlOOH,
Al₂O₃And Al (OH) ₃Is preferred and more preferred
In other words, it is industrially inexpensive and highly reactive.
And AlOOH. Of course, multiple aluminum compounds
It can also be used.

As a concrete cobalt source, for example, C
o (OH) ₂ , CoO, Co ₂ O ₃ , Co ₃ O ₄ , Co (O
_{Ac) 2 · 4H 2 O,} CoCl 2, Co (NO 3) 2 · 6H 2
O, and Co (SO ₄₎ various cobalt compounds such as ₂ · 7H ₂ O and the like. Among them, C is used because it does not generate harmful substances such as NOx and SOx during the firing process.
O (OH) ₂ , CoO, Co ₂ O ₃ , and Co ₃ O ₄ are preferable, and Co (OH) ₂ is more preferable because it is industrially available at low cost and has high reactivity. Of course, a plurality of cobalt compounds can be used.

As a concrete iron source, for example, FeO
(OH), Fe₂O₃, Fe₃O_Four, FeCl₂, FeC
l₃, FeC₂O_Four・ 2H₂O, Fe (NO₃)₃・ 9H
₂O, FeSO _Four・ 7H₂O and Fe₂(SO_Four)₃・ NH₂
Various iron compounds such as O can be mentioned. Above all,
No harmful substances such as NOx and SOx are generated during the firing process.
FeO (OH), Fe₂O₃, Fe₃O_FourIs good
More preferably, it is industrially available at low cost.
FeO (OH), Fe from the viewpoint of high reactivity₂O₃And
It Of course, it is also possible to use a plurality of iron compounds.

As a concrete magnesium source, for example,
For example, Mg (OH)₂, MgO, Mg (OAc)₂・ 4H₂
O, MgCl₂, MgC₂O_Four・ 2H₂O, Mg (NO₃)₂
・ 6H ₂O and MgSO_FourVarious magnesium compounds such as
I can list things. Above all, NO during the firing process
Mg, in that it does not generate harmful substances such as x and SOx
(OH)₂, MgO are preferable, and more preferably,
Mg is commercially available at low cost and has high reactivity.
(OH)₂Is. Of course, using multiple magnesium compounds
It can also be used.

As a concrete calcium source, for example,
Ca (OH) ₂ , CaO, Ca (OAc) ₂ · H ₂ O, C
aCo ₃ , CaC ₂ , CaC ₂ O ₄ · H ₂ O, CaCl ₂ , C
_{aWO 4, Ca (NO 3)} 2 · 4H 2 O, and CaSO ₄ ·
There may be mentioned various calcium compounds such as 2H ₂ O. Among them, Ca (OH) ₂ , CaO, and Ca (OH) ₂ are preferable because they do not generate harmful substances such as NOx and SOx during the firing process.
CaCo ₃ is preferable, and Ca (OH) ₂ is more preferable because it is industrially available at low cost and has high reactivity.
Is. Of course, a plurality of calcium compounds can also be used.

The molar ratio of lithium, nickel, manganese, and optionally a substituting element such as aluminum used at the time of charging may be appropriately selected so that the desired composition of the lithium nickel manganese composite oxide can be obtained. . These lithium source, nickel source, manganese source and substitutional element source are
It may be mixed as a raw material for firing by dry mixing,
It may be mixed as a wet type (that is, in a slurry) and then dried to be used as a raw material for firing. When mixed dry and used as a raw material for firing, it is necessary to perform multiple firings such as calcination, crushing and main firing in this order, and to crush during at least two firings of impurities. It is preferable in terms of suppressing generation and improving capacity.

The method of mixing and drying in the slurry when the mixture is wet-mixed and dried to be the raw material for firing will be described below. As the dispersion medium used in the slurry, various organic solvents and aqueous solvents can be used, but water is preferable. The total weight ratio of the lithium source, the nickel source, the manganese source and the substitutional element source to the total weight of the slurry is usually 10% by weight or more, preferably 12.5% by weight or more, usually 50% by weight or less, preferably 35% by weight.
It is the following. When the weight ratio is less than the above range, the slurry concentration is extremely dilute, so the spherical particles produced by spray drying become unnecessarily small or susceptible to breakage, while above the range, the slurry becomes uniform. It becomes difficult to maintain the sex.

The average particle size of the solid matter in the slurry is usually 2
μm or less, preferably 1 μm or less, more preferably 0.5 μm or less. If the average particle size of the solid matter in the slurry is too large, not only the reactivity in the firing step is lowered, but also the sphericity is lowered and the final powder packing density tends to be lowered. This tendency is 50μ in average particle size
This becomes particularly noticeable when it is attempted to produce granulated particles of m or less. Further, since making the particles smaller than necessary leads to an increase in the cost of pulverization, the average particle size of the solid is usually 0.01 μm or more, preferably 0.05 μm or more, more preferably 0.1 μm or more.

As a method for controlling the average particle size of the solid matter in the slurry, the raw material compound is previously dry pulverized by a ball mill, a jet mill or the like, and the raw material compound is dispersed in a dispersion medium by stirring or the like, or the raw material compound is dispersed. In addition, there may be mentioned a method of carrying out wet pulverization using a medium agitation type pulverizer or the like after dispersion by stirring or the like. It is preferable to use a method in which the raw material compound is dispersed in a dispersion medium and then wet-milled by using a medium agitation mill or the like. The effect of the present invention is remarkably exhibited by wet pulverization.

The viscosity of the slurry is usually 50 mPas.
-S or more, preferably 100 mPa-s or more, particularly preferably 200 mPa-s or more, usually 3000 mPa-s
The following is preferably 2000 mPa · s or less, and particularly preferably 1600 mPa · s or less. When the viscosity is less than the above range, a large load is applied to drying before firing,
While the spherical particles produced by drying become unnecessarily small or easily damaged, on the other hand, when it exceeds the above range, it becomes difficult to handle, for example, suction by a tube pump used for slurry transportation during drying becomes impossible. The viscosity of the slurry can be measured using a known BM type viscometer. The BM type viscometer is a measuring method that employs a method of rotating a predetermined metal rotor in a room temperature atmosphere. The viscosity of the slurry is calculated from the resistance force (twisting force) applied to the rotating shaft of the rotor when the rotor is rotated while being immersed in the slurry. However, the room temperature atmosphere means a temperature of 10 ° C to 35 ° C and a relative humidity of 20% RH to 80% RH.
Figure 7 illustrates a normally considered laboratory level environment.

The slurry thus obtained is usually dried and then subjected to a firing treatment. Spray drying is preferred as the drying method. By performing spray drying, a spherical lithium nickel manganese composite oxide can be obtained by a simple method, and as a result, the packing density can be improved. The method of spray drying is not particularly limited, but for example, a droplet of the slurry component from the nozzle by causing a gas flow and a slurry to flow into the tip of the nozzle (this may be simply referred to as “droplet” in this specification). is there.)
Can be used to rapidly dry the scattered droplets by using an appropriate drying gas temperature and blowing amount. Air, nitrogen or the like can be used as the gas supplied as the gas flow, but air is usually used. It is preferable to use these under pressure. The gas flow has a gas linear velocity of usually 100 m / s or more, preferably 20 m / s or more.
The injection is performed at 0 m / s or more, more preferably 300 m / s or more. If it is too small, it becomes difficult to form appropriate droplets. However, since it is difficult to obtain a too high linear velocity,
The normal injection speed is 1000 m / s or less. The nozzle used may have any shape as long as it can eject minute liquid droplets, and a conventionally known one, for example, a liquid droplet described in Japanese Patent No. 2977080 can be miniaturized. Such nozzles can also be used. In addition, it is preferable that the droplets are sprayed in an annular shape from the viewpoint of improving productivity. The scattered droplets are dried. As described above, treatment such as appropriate temperature and air blowing is performed so as to quickly dry the scattered droplets, but it is preferable to introduce the drying gas from the upper part of the drying tower to the lower part by downflow. With such a structure, the throughput per unit volume of the drying tower can be greatly improved. Also,
When spraying liquid droplets in a substantially horizontal direction, by suppressing the liquid droplets sprayed in the horizontal direction with downflow gas, it is possible to greatly reduce the diameter of the drying tower, making it possible to manufacture inexpensively in large quantities. Becomes The dry gas temperature is
It is usually 50 ° C or higher, preferably 70 ° C or higher, and usually 12
The temperature is 0 ° C or lower, preferably 100 ° C or lower. If the temperature is too high, the resulting granulated particles will have many hollow structures, and the packing density of the powder will tend to decrease, while if it is too low, the powder will stick to the powder due to water condensation at the powder outlet. Problems such as blockages may occur.

By spray-drying in this manner, granulated particles as a raw material can be obtained. As the granulated particle size,
The average particle size is preferably 50 μm or less, more preferably 30 μm or less. However, since it tends to be difficult to obtain a too small particle diameter, it is usually 4 μm or more, preferably 5 μm or more. The particle size of the granulated particles can be controlled by appropriately selecting the spray type, pressurized gas flow supply rate, slurry supply rate, drying temperature and the like.

The raw material containing lithium, manganese, and nickel is subjected to firing treatment. The firing conditions are important for controlling the specific surface area and powder packing density specified in the present invention. Depending on the raw material composition, the tendency is that if the firing temperature is too high, the tap density becomes too large, and conversely if it is too low, the tap density becomes too small and the specific surface area becomes too large. Further, when the molar ratio of nickel in the total of nickel, manganese, and transition metal is large, the relatively optimum firing temperature tends to be low. The firing temperature varies depending on the type of lithium source, manganese source, nickel source, etc. used as the raw material, but is usually 700 ° C. or higher, preferably 725 ° C. or higher, and more preferably 750 ° C.
C. or higher, more preferably 800.degree. C. or higher, and usually 1050.degree. C. or lower, preferably 1000.degree. C. or lower, more preferably 950.degree. C. or lower, most preferably 900.degree. C. or lower.

Although the firing time varies depending on the temperature, it is usually 30 minutes or more and 50 hours or less in the above temperature range. If the firing time is too short, it becomes difficult to obtain a lithium nickel manganese composite oxide having good crystallinity, and if it is too long, it is not practical. If the firing time is too long,
Further, it is preferably 25 hours or less, and more preferably 20 hours or less, because crushing becomes necessary thereafter or crushing becomes difficult.

In order to obtain a lithium nickel manganese composite oxide with few crystal defects, it is preferable to cool slowly after the firing reaction, for example, 5 ° C./min. It is preferable to gradually cool at the following cooling rate. The atmosphere during firing can be an oxygen-containing gas atmosphere such as air or an inert gas atmosphere such as nitrogen or argon depending on the composition and structure of the compound to be produced. The nickel is preferably air, oxygen-enriched air or oxygen because it needs to be oxidized from divalent raw material to trivalent desired product.

The heating device used for firing is the above-mentioned temperature,
There is no particular limitation as long as the atmosphere can be achieved, and for example, a box furnace, a tubular furnace, a tunnel furnace, a rotary kiln or the like can be used. In the present invention, the average particle size of the solid content in the slurry, the average particle size of the granulated particles after spray drying, and the average particle size of the lithium nickel manganese composite oxide are known laser diffraction / scattering particle sizes. It is measured by a distribution measuring device. The measurement principle of this method is as follows. That is, slurry or powder is dispersed in a dispersion medium, the sample solution is irradiated with laser light, and scattered light that is incident on particles and scattered (diffracted) is detected by a detector. The scattering angle θ (angle between the incident direction and the scattering direction) of the detected scattered light is forward scattering (0 <θ <
90 °), and side scattering or back scattering (90 ° <θ <180 °) for small particles. From the measured angular distribution value, the particle size distribution is calculated using information such as the incident light wavelength and the particle refractive index. Further, the average particle size is calculated from the obtained particle size distribution. The dispersion medium used in the measurement may be, for example, a 0.1 wt% sodium hexametaphosphate aqueous solution.

A lithium secondary battery can be produced by using the lithium nickel manganese composite oxide of the present invention as a positive electrode active material (positive electrode material). A lithium secondary battery usually has a positive electrode, a negative electrode, and an electrolyte layer. Examples of the secondary battery of the present invention include a secondary battery consisting of a positive electrode, a negative electrode, an electrolytic solution, and a separator, in which case there is an electrolyte between the positive electrode and the negative electrode, and the separator has a positive electrode and a negative electrode. Placed between them so that they do not touch.

The positive electrode usually contains the lithium nickel manganese composite oxide and a binder. Also usually
The positive electrode is formed by forming a positive electrode layer containing the lithium nickel manganese composite oxide and a binder on a current collector. Such a positive electrode layer can be produced by applying a slurry of a lithium nickel manganese composite oxide, a binder and, if necessary, a conductive agent and the like in a solvent to a positive electrode current collector and drying.

The positive electrode layer may further contain an active material capable of inserting and extracting lithium ions other than the lithium nickel manganese composite oxide, such as LiFePO ₄ . The ratio of the active material in the positive electrode layer is usually 10% by weight.
Or more, preferably 30% by weight or more, more preferably 5
It is 0% by weight or more, usually 99.9% by weight or less, and preferably 99% by weight or less. If it is too large, the mechanical strength of the electrode tends to be poor, and if it is too small, the battery performance such as capacity tends to be poor.

The binder used for the positive electrode is, for example, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, EPDM.
(Ethylene-propylene-diene terpolymer), SB
Examples thereof include R (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluororubber, polyvinyl acetate, polymethylmethacrylate, polyethylene and nitrocellulose. The proportion of the binder in the positive electrode layer is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 5% by weight or more, and usually 80% by weight or less, preferably 60% by weight or less, more preferably It is 40% by weight or less, and most preferably 10% by weight or less. If the proportion of the binder is too low, the active material cannot be sufficiently retained and the mechanical strength of the positive electrode is insufficient, which may deteriorate the battery performance such as cycle characteristics, while if it is too high, the battery capacity and conductivity are reduced. Sometimes.

The positive electrode layer usually contains a conductive agent in order to enhance conductivity. Examples of the conductive agent include graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, and carbon materials such as amorphous carbon such as needle coke. The proportion of the conductive agent in the positive electrode is usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 1% by weight or more and usually 50% by weight or less, preferably 30% by weight or less, It is preferably 15% by weight or less. If the proportion of the conductive agent is too low, the conductivity may be insufficient, and conversely, if it is too high, the battery capacity may decrease.

The slurry solvent is not particularly limited as long as it dissolves or disperses the binder, but an organic solvent is usually used. For example, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methylethylketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN
-Dimethylaminopropylamine, ethylene oxide,
Tetrahydrofuran etc. can be mentioned. It is also possible to add a dispersant, a thickener and the like to water to make the active material into a slurry with a latex such as SBR.

The thickness of the positive electrode layer is usually 1 to 1000 μm,
It is preferably about 10 to 200 μm. If it is too thick, the conductivity tends to decrease, and if it is too thin, the capacity tends to decrease. As the material of the current collector used for the positive electrode, aluminum, stainless steel, nickel-plated steel or the like is used, and aluminum is preferable. The thickness of the current collector is usually 1 to 1000 μm, preferably 5 to 500 μm
It is a degree. If it is too thick, the capacity of the lithium secondary battery as a whole may be reduced, and if it is too thin, the mechanical strength may be insufficient.

The positive electrode layer obtained by coating and drying is preferably compacted by a roller press or the like in order to increase the packing density of the active material. The negative electrode active material used for the negative electrode of the secondary battery may be lithium or a lithium alloy such as a lithium aluminum alloy, but a carbon material having higher safety and capable of absorbing and releasing lithium is preferable.

The carbon material is not particularly limited, but graphite, coal-based coke, petroleum-based coke, coal-based pitch carbide, petroleum-based pitch carbide, or carbide obtained by oxidizing these pitches, needle coke, pitch coke. Examples thereof include phenolic resins, carbides such as crystalline cellulose, and carbon materials obtained by partially graphitizing these, furnace black, acetylene black, pitch-based carbon fibers, and the like.

Further, as the negative electrode active material, SnO, SnO
₂, Sn_1-xM_xO (M = Hg, P, B, Si, Ge
Is Sb, where 0 ≦ x <1), Sn₃O₂(OH)₂ , S
n_{3- x}M_xO₂(OH)₂(M = Mg, P, B, Si, G
e, Sb or Mn, where 0 ≦ x <3), LiSi
O₂, SiO₂Or LiSnO₂Can be mentioned
It In addition, a mixture of two or more selected from these
You may use as a negative electrode active material.

The negative electrode is usually formed by forming a negative electrode layer on a current collector as in the case of the positive electrode. The binder used at this time, and the conductive agent and the like used as necessary and the slurry solvent may be the same as those used for the positive electrode. Further, as the current collector of the negative electrode, copper, nickel, stainless steel, nickel-plated steel or the like is used, and preferably copper is used.

When a separator is used between the positive electrode and the negative electrode, a microporous polymer film is used, and polytetrafluoroethylene, polyester, nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyfluorine is used. Polyolefin polymers such as vinylidene, polypropylene, polyethylene and polybutene can be used. Further, a non-woven filter of glass fiber or the like, or a non-woven filter of glass fiber and polymer fiber can also be used. The chemical and electrochemical stability of the separator is an important factor. From this point of view, the polyolefin-based polymer is preferable, and from the viewpoint of the self-closing temperature which is one of the purposes of the battery separator, it is preferable to be made of polyethylene.

In the case of the polyethylene separator, ultrahigh molecular weight polyethylene is preferable from the viewpoint of shape retention at high temperature, and the lower limit of its molecular weight is preferably 500,000, more preferably 1,000,000, and most preferably 1,500,000. On the other hand, the upper limit of the molecular weight is preferably 5,000,000, more preferably 4,000,000, and most preferably 3,000,000. This is because if the molecular weight is too large, the fluidity is so low that the pores of the separator may not be closed when heated.

As the electrolyte that constitutes the electrolyte layer in the lithium secondary battery of the present invention, for example, a known organic electrolytic solution, polymer solid electrolyte, gel electrolyte, inorganic solid electrolyte, etc. can be used. Organic electrolytes are preferred. The organic electrolytic solution is composed of an organic solvent and a solute. The organic solvent is not particularly limited, for example, carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, chlorinated hydrocarbons,
Ethers, amines, esters, amides, phosphoric acid ester compounds and the like can be used. Typical examples of these are dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 4-methyl-2. -Pentanone, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propio Nitrile, benzonitrile, butyronitrile, valeronitrile, 1,2-dichloroethane, dimethylformamide, dimethyl sulfoxide, trimethyl phosphate, triethyl phosphate, etc. alone or A mixed solvent of two or more can be used.

The above organic solvent preferably contains a high dielectric constant solvent in order to dissociate the electrolyte. Here, the high dielectric constant solvent has a relative dielectric constant of 20 at 25 ° C.
The above compounds are meant. In the high dielectric constant solvent, it is preferable that the electrolytic solution contains ethylene carbonate, propylene carbonate, and a compound in which hydrogen atoms thereof are replaced by another element such as halogen or an alkyl group. The ratio of the high dielectric constant compound in the electrolytic solution is preferably 20.
It is at least 30% by weight, more preferably at least 30% by weight, and most preferably at least 40% by weight. This is because if the content of the compound is small, desired battery characteristics may not be obtained.

The solute to be dissolved in this solvent is not particularly limited, but any conventionally known solute can be used, such as LiClO ₄ , LiAsF ₆ , LiPF ₆ and LiB.
F ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl, LiBr, CH ₃
SO ₃ Li, CF ₃ SO ₃ Li, LiN (SO ₂ CF ₃ ) ₂ ,
LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , L
iN (SO ₃ CF ₃ ) _{2 and the} like can be used, and at least one or more of these can be used. Also, C
Gases such as O ₂ , N ₂ O, CO, and SO ₂ and polysulfide S _x ^2-, such as the above additives alone, in any proportion, are additives that form a good film that enables efficient charging and discharging of lithium ions on the negative electrode surface. Alternatively, it may be added to the mixed solvent.

When the polymer solid electrolyte is used, the known polymer can be used. In particular, it is preferable to use a polymer having high ionic conductivity with respect to lithium ions, and for example, polyethylene oxide, polypropylene oxide, polyethyleneimine and the like are preferably used. It is also possible to add the above solvent to the polymer together with the above solute and use it as a gel electrolyte.

Even when an inorganic solid electrolyte is used, this
Use of known crystalline and amorphous solid electrolytes for inorganic substances
You can Examples of the crystalline solid electrolyte include Li
I, Li₃N, Li_{1 + x}M_xTi_2-x(PO_Four)₃(M = A
l, Sc, Y, La), Li_{0.5- 3x}RE_{0.5 + x}TiO
₃(RE = La, Pr, Nd, Sm), etc.
As the crystalline solid electrolyte, for example, 4.9 LiI-3
4.1 Li₂O-61B₂O_Five, 33.3Li₂O-66.
7 SiO₂Oxide glass such as 0.45LiI-0.3
7Li₂S-0.26B₂S₃, 0.30LiI-0.4
2 Li₂S-0.28SiS ₂Such as sulfide glass
To be Use at least one of these
You can

[0057]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. <Example 1> LiOH.H ₂ O, Ni (OH) ₂ , Mn ₂
O ₃ and Co (OH) ₂ are the compositions in the final layered lithium nickel manganese composite oxide, and Li: Ni: M
n: Co = 1.03: 0.60: 0.30: 0.10.
(Mole ratio) was weighed, and pure water was added to this to prepare a slurry having a solid content concentration of 16% by weight. While stirring this slurry, a circulation type medium stirring type wet pulverizer (manufactured by Shinmaru Enterprises Co., Ltd .: Dyno Mill KDL-A)
Type) for 2 hours. The viscosity of this slurry was measured with a BM type viscometer (manufactured by Tokimec). The measurement is carried out in the atmosphere at room temperature, a specific metal rotor is fixed to the rotating shaft of the main body of the device, the rotor is immersed below the liquid surface of the slurry, and the rotating shaft is rotated to generate a resistance force (twisting force) on the rotor. The viscosity was calculated. As a result, the initial viscosity is 1
It was 150 mPa · s.

Next, this slurry was spray-dried using a two-fluid nozzle type spray dryer (manufactured by Okawara Kakohki Co., Ltd .: L-8 type spray dryer). Air was used as the dry gas at this time, and the dry gas introduction rate was 40 m ³ / mi.
n, the inlet temperature of the dry gas was 85 ° C. Then, the granulated particles obtained by spray drying were fired in air at 800 ° C. for 10 hours to obtain a lithium nickel manganese composite oxide having a molar ratio composition almost charged. <Example _{2> LiOH · H 2 O,} Ni (OH) 2, Mn 2
O ₃ and Co (OH) ₂ are the compositions in the final layered lithium nickel manganese composite oxide, and Li: Ni: M
n: Co = 1.03: 0.65: 0.15: 0.20
A lithium-transition metal composite oxide was obtained in the same manner as in Example 1, except that the weight ratio was adjusted to (molar ratio). The initial viscosity was 800 mPa · s. <Example _{3> LiOH · H 2 O,} Ni (OH) 2, Mn 2
O ₃ and Co (OH) ₂ are the compositions in the final layered lithium nickel manganese composite oxide, and Li: Ni: M
n: Co = 1.03: 0.75: 0.15: 0.10.
A lithium-transition metal composite oxide was obtained in the same manner as in Example 1, except that the weight ratio was adjusted to (molar ratio). The initial viscosity was 850 mPa · s. <Example _{4> LiOH · H 2 O,} Ni (OH) 2, Mn 2
O ₃ and Co (OH) ₂ are the compositions in the final layered lithium nickel manganese composite oxide, and Li: Ni: M
n: Co = 1.03: 0.50: 0.25: 0.25
(Molar ratio) and the firing conditions are 90
A lithium transition metal composite oxide was obtained in the same manner as in Example 1 except that the temperature was set to 0 ° C. for 10 hours. Initial viscosity is 800 mP
It was a.s. <Example _{5> LiOH · H 2 O,} Ni (OH) 2, Mn 2
O ₃ and Co (OH) ₂ are the compositions in the final layered lithium nickel manganese composite oxide, and Li: Ni: M
n: Co = 1.03: 0.60: 0.30: 0.10.
(Molar ratio), the firing atmosphere was 900 ° C. for 10 hours under oxygen flow (sample amount 10 g, oxygen flow amount 0.5).
L / min. A lithium-transition metal composite oxide was obtained in the same manner as in Example 1 except that <Comparative Example 1> LiOH.H ₂ O and Ni / Mn coprecipitate (molar ratio 1/1, manufactured by Tanaka Chemical Co., Ltd.) each in the final layered lithium nickel manganese composite oxide composition,
Li: Ni: Mn: Co = 1.03: 0.50: 0.5
Weigh it so that it becomes 0 (molar ratio), and set the firing conditions in air to 8
A lithium-transition metal composite oxide was obtained in the same manner as in Example 1 except that the temperature was set to 00 ° C. for 10 hours. <Comparative Example 2> A lithium transition metal composite oxide was obtained in the same manner as in Comparative Example 1 except that the firing conditions were 900 ° C and 10 hr in air. <Comparative Example 3> A lithium transition metal composite oxide was obtained in the same manner as in Comparative Example 1 except that the firing conditions were 1000 ° C and 10 hr in air. <Comparative Example 4> A lithium transition metal composite oxide was obtained in the same manner as in Example 4 except that the firing conditions were 700 ° C and 10 hr in air. <Comparative Example 5> A lithium transition metal composite oxide was obtained in the same manner as in Example 2 except that the firing conditions were 1000 ° C and 10 hr in air.

The powder X-ray diffraction of the lithium nickel manganese composite oxides obtained in Examples 1-5 and Comparative Examples 1-5 was measured and found to have the structure of a rhombohedral lithium nickel manganese composite oxide. Was confirmed. <Powder Packing Density and Specific Surface Area> Table 1 shows the powder packing density and specific surface area of the obtained powder of lithium nickel manganese composite oxide. Powder packing density is 10 for 5g of powder
It was measured by putting it in a ml glass graduated cylinder and tapping it 200 times. The BET type powder specific surface area measuring device (Okura Riken: AMS8000 type fully automatic powder specific surface area measuring device) was used for the measurement of the specific surface area.

[0060]

[Table 1] <Production of Positive Electrode, Capacity Check, and Rate Test> Examples 1 to 5
And the lithium nickel manganese cobalt composite oxides obtained in Comparative Examples 1 to 5 were weighed at a ratio of 75% by weight, acetylene black 20% by weight, and polytetrafluoroethylene powder 5% by weight, sufficiently mixed in a mortar to thinly The sheet-shaped product was punched using a 9 mmφ punch. At this time, the total weight was adjusted to be about 8 mg. This was pressed onto an expanded metal of Al to obtain a positive electrode.

A coin cell was assembled using the obtained positive electrode as a test electrode and Li metal as a counter electrode. That is, a positive electrode (12 mmφ) is placed on a positive electrode can, a porous polyethylene film having a thickness of 25 μm is placed thereon as a separator, and a negative electrode is placed after pressing with a polypropylene gasket.
After placing a spacer for adjusting the thickness, as a non-aqueous electrolyte solution, 1 mol / L lithium hexafluorophosphate (LiP
A mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) having a volume fraction of 3: 7 in which F ₆ ) was dissolved was used as an electrolytic solution, and this was added to the inside of the battery to allow it to sufficiently soak, and then the negative electrode can was The battery was sealed.

Then, a constant current charge of 0.2 mA / cm ² , that is, a reaction for releasing lithium ions from the positive electrode was carried out at an upper limit of 4.3 V, and then a constant current discharge of 0.5 mA / cm ² was carried out, that is, the positive electrode was charged with lithium. The initial charge capacity Q _c mAh / g per unit weight of the positive electrode active material and the initial discharge capacity Q _d1 mAh / g, 11 mA / cm ² when the reaction of occluding ions is carried out at a lower limit of 3.0 V or 3.2 V Discharge capacity Q _d2 m
Ah / g is shown together with the upper and lower limit voltages of charge and discharge. Table 2 shows the initial charge / discharge capacity.

[0063]

[Table 2] As is clear from Table-1 and Table-2, the specific surface area is 3.
5 m ² / g or less and a powder packing density of 1.4-2.8 g
When it is / cm ^3, it is possible to provide a positive electrode active material exhibiting excellent battery performance.

[0064]

According to the present invention, a lithium nickel manganese composite oxide for a lithium secondary battery having excellent battery characteristics, high capacity per volume and high energy density can be obtained. It is possible to obtain a lithium nickel manganese composite oxide that is excellent in battery performance such as rate characteristics and cycle characteristics, has high safety, and is inexpensive and is used in a lithium secondary battery. In particular, according to the present invention, it is possible to obtain a lithium nickel manganese composite oxide which is excellent in discharge capacity at a large current and which can be used in a lithium secondary battery having a high volume energy density.

Continued front page    F-term (reference) 4G048 AA04 AA05 AB05 AC06 AD03                       AD06 AE05                 5H029 AJ02 AJ03 AK03 AL02 AL03                       AL06 AL07 AL08 AL12 AM03                       AM04 AM07 AM16 HJ02                 5H050 AA02 AA08 BA16 BA17 CA08                       CA09 CB01 CB02 CB07 CB08                       CB09 CB12 DA02 EA24 HA07

Claims (7)

[Claims] 1. A lithium nickel manganese composite oxide represented by the following general formula (1) having a specific surface area of 3.5.
m ² / g or less and the powder packing density is 1.4-2.8 g /
A lithium nickel manganese composite oxide characterized by having a size of cm ³ . Embedded image Li _X Ni _Y Mn _Z Q _(1-YZ) O ₂ (1) (In the formula, X represents a number in the range of 0 <X ≦ 1.2. Y and Z are 1 ≦ Y / Z ≦ 9 and 0 <(1−Y−Z) ≦
It represents a number that satisfies the relationship of 0.5. Q is Co, Al, F
represents at least one selected from the group consisting of e, Mg, Ga, Ti and Ca. ) 2. The lithium nickel manganese composite oxide according to claim 1, which has a specific surface area of 0.2 m ² / g or more. 3. The lithium nickel manganese composite oxide according to claim 1, wherein Q in the general formula (1) contains Co. 4. The lithium nickel manganese composite oxide according to claim 1, wherein the value of (1-YZ) in the general formula (1) is 0.01 or more. 5. A positive electrode material for a lithium secondary battery, containing the lithium nickel manganese composite oxide according to claim 1. 6. A positive electrode for a lithium secondary battery, comprising the lithium nickel manganese composite oxide according to claim 1 and a binder. 7. A lithium secondary battery comprising a positive electrode using the lithium nickel manganese composite oxide according to claim 1, a negative electrode, and an electrolyte.